[R-390] HP 8640B Question

[Mahlon Haunschild]

Indeed, that ext. counter input is spec'd from 100 mVrms to 1.3Vrms.  That
last one is very clearly marked as a "may-not-exceed" in the service manual.

Also, its Zin is 50 ohms, another way to get things messed up.

It leaves the cap on or it gets hosed!

regards,

Mahlon - K4OQ

> ------------------------------------------------------------------------
> 
> Subject:
> Re: [R-390] HP 8640B Question
> From:
> 2002tii <bmw2002tii at nerdshack.com>
> Date:
> Sat, 20 Feb 2010 16:07:59 -0500
> To:
> r-390 at mailman.qth.net
> 
> To:
> r-390 at mailman.qth.net
> 
> 
> Bob wrote:
> 
> <snip>
 >
> That said, most 8640s I've seen that read all zeros don't do so because 
> the counter input is set to EXT, but rather because someone once used 
> them to count external signals and fried the counter.  That is the 
> single most common 8640 problem I've seen.  So much so that I advise 
> folks NEVER to use the 8640's external counter.  It comes with a BNC cap 
> -- leave it there.  Note that the military Option 323 units do not have 
> an external counter input, for this very reason.
> 
> Best regards,
> 
> Don
>